PERMUTATION & COMBINATION | IIT JEE CONCEPT | Part 11 | JEE Advance 2014 | Number of Lines Diagonals - Videos

In this video, we will learn an important concept of counting the number of lines in two cases:
(i) When all the points given are non-collinear
(ii) When some of the points or a set of points are collinear
Also, I will discuss how to count the number of diagonals in a n-sided polygon and number of handshakes.

Questions Discussed
JEE Advanced 2014
Let n ≥ 2 be an integer. Take n distinct points on a circle and join each pair of points by a line segment. Colour the line segment joining every pair of adjacent points by blue and the rest by red. If the number of red and blue line segments are equal, then the value of n is
Answer: 5

TRY YOURSELF Questions
Question 1
Consider 6 vertices of a regular hexagon and its centre. How many: (i) Straight lines (ii) triangles can be formed using these 7 points.
Answers: (i) 15 (ii) 32

Question 2
The number of diagonals that can be drawn in an octagon is
(A) 16 (B) 20 (C) 28 (D) 40
Answer: (B)

Question 3
On sides AB, BC and AC of a triangle ABC, 3, 4, 5 distinct points (excluding vertices) are chosen. Find the number of straight lines that can be constructed.
Answers: 50

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